This project is directed towards the definition of several factors in DNA synthesis: 1) in vitro analysis of dnaB mutational defects, 2) in vivo analysis of dnaB mutational defects, 3) in vivo complementation of the Gro-character of some dnaB alleles, 4) construction of a DNA synthesis interaction map, and 5) the isolation of new dna mutants. To date, we have shown that dnaB mutations result in the accumulation of small, 4S intermediates in DNA replication that are joined together in vitro via an NMN-insensitive ligating reaction. The interaction map to discern the hypothesized interactions between proteins in the chromosome replication machinery is to be approached in two ways: 1) the effect on the Gro-phenotype, which alters the growth of lambda bacteriophage, in dna double mutants and 2) by external suppression of dnaB mutations. New dna mutants will be isolated from a carefully prepared new parental strain which has been constructed.